An ion thruster is a form of electric propulsion used for spacecraft propulsion that creates thrust by accelerating ions. The term is used to refer to gridded ion thrusters, but may often be applied to all electric propulsion systems that accelerate plasma (electrically neutral medium of positive and negative particles), since plasma consists of ions. Ion thrusters are categorized by how they accelerate the ions, using either electrostatic or electromagnetic force. Electrostatic ion thrusters use the Coulomb force (the electric field vector at that point) and accelerate the ions in the direction of the electric field. Electromagnetic ion thrusters use the Lorentz force (the combination of electric and magnetic force on a point charge due to electromagnetic fields) to accelerate the ions.
Ion thrusters use beams of ions (electrically charged atoms or molecules) to create thrust in accordance with momentum conservation. The method of accelerating the ions varies, but all designs take advantage of the charge/mass ratio of the ions. This ratio means that relatively small potential differences can create very high exhaust velocities. This reduces the amount of reaction mass or fuel required, but increases the amount of specific power required, compared to chemical rockets. Ion thrusters are therefore able to achieve extremely high specific impulses. The drawback of the low thrust is low spacecraft acceleration, because the mass of current electric power units is directly correlated with the amount of power given. This low thrust makes ion thrusters unsuited for launching spacecraft into orbit, but ideal for in-space propulsion applications.
The applications of ion thrusters include control of the orientation and position of orbiting satellites (some satellites have dozens of low-power ion thrusters), and they are used as a main propulsion engine for low-mass space vehicles (for example, “Deep Space 1”, and “Dawn”).
Various ion thrusters have been designed, and they all generally fall under two categories: electrostatic or electromagnetic. The main difference is how the ions are accelerated. Electrostatic ion thrusters use the Coulomb force, and are categorized as accelerating the ions in the direction of the electric field. Electromagnetic ion thrusters use the Lorentz force to accelerate the ions.
Power supplies for ion thrusters may be solar panels, but at sufficiently large distances from the sun, other power sources may be used. In such cases, the power supply mass is essentially proportional to the peak power that can be supplied, and they both essentially give, for this application, no limit to the energy. Electric thrusters tend to produce low thrust, which results in low acceleration. Using g0 as 9.81 m/s2; “F=m a”; or “a=F/m” (where “F” stands for force, “m” for mass, and “a” for acceleration), a thruster producing a thrust (=force) of 92 mN will accelerate a satellite with a mass of 1,000 kg by 0.092/1,000=0.000092 m/s2.
NASA (National Aeronautics and Space Administration) has used ion thrusters in its spacecrafts. For example, the NASA Solar electric propulsion Technology Application Readiness (NSTAR), with 2.3 kW was used on two successful missions. Or, to give another example: NASA's Evolutionary Xenon Thruster (NEXT), with a 6.9 kW ion thruster.
NASA's ion thruster NSTAR program provided the technology used on the “Deep Space 1” spacecraft. The NSTAR 30 cm ion thruster operates over a 0.5 kW to 2.3 kW input power range, providing thrust from 19 mN to 92 mN. The specific impulse ranges from 1,900 s at 0.5 kW to 3,100 s at 2.3 kW.
Due to the relatively high power needs of ion thrusters, the specific power of their power supplies, and the requirement for an environment void of other ionized particles, the general use of ion thrust propulsion is currently only practical in space.
All the methods described above have not yet provided satisfactory solutions to the problem of increasing the thrust power of ion thrusters.
In one aspect of the invention, the invention provides an ion thruster that can be operated within the earth's atmosphere.
In another aspect of the invention, the invention provides an ion thruster that is efficient to power a vehicle within the earth's atmosphere.
In another aspect of the invention, the invention provides an ion thruster that is practical for use as the engine for powering vehicles on the surface of the earth.
In another aspect of the invention, the invention provides an ion thruster with a propeller for increasing the resulting thrust.
In another aspect of the invention, the invention provides a solution to the above-mentioned and other problems of the prior art.
Other aspects of the invention will become apparent as the description proceeds.